The present invention relates to a variable-diameter power-transmission device, and also to a continuously-variable drive including such transmission device. The invention is particularly useful with respect to continuously-variable drives for automotive vehicles and is therefore described below with respect to that application, but it will be appreciated that the invention, or various features thereof, could advantageously be used in other applications as well.
A number of continuously-variable drives are known for changing the speed of a driven device with respect to the driving device. One popular drive for automotive vehicles includes an automatic transmission having a plurality of gears selectively engageable for changing the speed of the vehicle, but in such transmissions the transmission ratio is changed in steps, each step having a fixed transmission ratio. A number of stepless continuously-variable transmissions are known, e.g. those using cone-shaped pulley wheels, but such transmissions are usually not very efficient, for example because of slippage between the belt and the pulley wheels.
Among the disadvantages of the fixed-ratio transmission systems commonly used today are: (1) the transmission system is complicated, expensive, and costly in maintenance; (2) undue energy losses are produced in the transmission system, particularly when not driving at the most efficient portion of the speed-change range of the transmission; (3) high fuel consumption is involved, which is evident by the substantially higher fuel consumption of automatic transmission vehicles as compared to manual-transmission vehicles.